Reformed gas production method and reformed gas production apparatus

ABSTRACT

The present invention relates to a reformed gas production apparatus that includes a reaction chamber containing a reforming catalyst, a supply route to the reaction chamber, a reformed gas conduction route from the reaction chamber, and a reaction chamber temperature control means that controls a temperature of the reaction chamber. The supply route supplies a fluid that includes a fuel containing a hydrocarbon having at least two carbon atoms, at least one of steam and a carbon dioxide-containing gas, and an oxygen-containing gas. The fuel can be a mixed fuel that includes a plurality of types of hydrocarbons that each have at least two carbon atoms. The reaction chamber temperature control means relates to the thermal decomposition index temperature of the fuel, which defines an upper limit temperature of the reforming reaction region.

CROSS REFERENCE TO RELATED PATENT APPLICATION

The present patent application is a divisional of U.S. patentapplication Ser. No. 11/630,929, having a PCT filing date of Jun. 28,2005, and a 35 U.S.C. §371(c)(1), (2), (4) date of Jul. 9, 2008, thedisclosure of which is incorporated herein by reference in its entirety.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention is related to reformed gas production methods andreformed gas production apparatuses for reforming hydrocarbon fuels toproduce a synthesis gas that includes hydrogen and carbon monoxide.

2. Description of Related Art

This synthesis gas can be produced by reforming hydrocarbons ormethanol, for example, and a reformed gas production apparatus thatproduces synthesis gas through such fuel reforming can be employed inthe fields of synthesis gas production, such as the production of liquidfuel from natural gas (GTL), and the production of hydrogen for fuelcells, for example.

Currently, the three methods of steam reforming, partial oxidation, andautothermal reforming, which combines these two methods, are the primarymethods for reforming hydrocarbon fuels.

Steam reforming is primarily used in the field of hydrogen productionbecause of the high H₂/CO ratio in the synthesis gas that it yieldsthrough Equation 1 below, and is employed for many applications. Becausehydrogen is created from not only the hydrocarbon but also from thesteam, there is a high H₂/CO ratio, making this method effective for theproduction of hydrogen. On the other hand, being an endothermicreaction, the addition of heat from the outside becomes therate-limiting factor and prevents the gas-space velocity (gasflow/catalyst amount) from being made large.C_(n)H_(2n+2) +nH₂O→(2n+1)H₂ +nCO  [Eq. 1]

Partial oxidation (also known as partial combustion) is an exothermicreaction in which, as shown by Equation 2 below, fuel is partiallyoxidized (partial combustion) to produce hydrogen. This method isadvantageous in that the reaction rate is fast and in that a largegas-space velocity can be achieved, while on the other hand its lowthermal efficiency is one drawback to this method.C_(n)H_(2n+2)+0.5nO₂→(n+1)H₂ +nCO  [Eq. 2]

Partial oxidation yields a synthesis gas whose H₂/CO ratio is lower thanthat of the synthesis gas produced by steam reforming, and is effectivefor instances where a low H₂/CO ratio is preferable for the applicationin which the synthesis gas will be used. When fuel is reformed throughpartial oxidation, however, at the same time that hydrocarbons such asmethane are reformed they may undergo dehydrogenation/oxidation andbecome heavy hydrocarbons or carbon, making continuous operationdifficult and, as mentioned above, the thermal efficiency of partialoxidation is poor. Together these make it difficult for partialoxidation to be adopted as the method for reforming natural gas andnaphtha, for example.

Autothermal reforming is a composite system in which the partialoxidation reaction and the steam reforming reaction are run in series orsimultaneously to supply the heat required for the endothermic steamreforming reaction using the heat produced through partial oxidation.Generally there are two types of such systems. One is a series method ofperforming the partial oxidation reaction in the gas phase using aburner or the like and then performing steam reformation (hereinafter,abbreviated as ATR). The other is a method of running partial oxidationand steam reformation simultaneously using a catalyst (hereinafter,abbreviated as CPO). Methods for producing hydrogen or synthesis gasusing these autothermal reforming methods have been disclosed in variouspublications (see JP 2000-84410A (pg. 2 to 14) and JP 2001-146406A (pg.2 to 6)).

One problem with fuel reforming by an autothermal reforming method isthat if the raw material is a hydrocarbon that has two or more carbonatoms, then there is much more pronounced carbon deposition near theinlet of the reformer than if methane is the raw material. That is, asshown in FIG. 17, the temperature near the inlet of the reformer risesabruptly due to the partial combustion of the hydrocarbon with oxygen,and this thermally decomposes hydrocarbons having two or more carbonatoms into carbon. For example, the working examples and comparativeexamples of JP 2001-146406A are examples in which carbon deposition wasconfirmed, and a conceivable reason for this is that the suddenelevation in the temperature of the catalyst layer inlet portion withinthe reaction chamber led to thermal decomposition of the hydrocarbon andsubsequent carbon deposition.

In some instances, a pre-reformer is set up at an early stage as one wayto solve the problem of fuel reforming by an autothermal reformingmethod (that being carbon deposition). Steam reformation and CPO areexamples of reforming methods that may be performed at the pre-reformer(see JP 2002-97479A (pg. 2 to 5)). An autothermal reformer withpre-reformer such as that shown in FIG. 18 has been proposed as a steamreforming pre-reformer. That is, in the pre-reformer, the hydrocarbonsare reformed into methane at a low temperature at which carbondeposition caused by steam reformation does not occur, and then themethane is reformed in an autothermal reformer and thereby convertedinto hydrogen and carbon monoxide. JP 2002-97479A discloses a CPOpre-reformer+ATR technology and mentions that all higher-orderhydrocarbons are converted during CPO. It is clear that this technologyis to be practiced under the premise that saturated hydrocarbons havingtwo or more carbon atoms are converted by CPO.

However, this autothermal reformer with pre-reformer has the problemthat if the pre-reformer is adopted for steam reforming, then the steamreforming reaction, whose rate of reaction is slower than that of thepartial oxidation reaction, is performed at low temperatures, thusrequiring large amounts of catalyst and therefore not allowing thereformer to be provided compact. Additionally, there is also the problemthat if this autothermal reformer with pre-reformer is employed in thereforming system of an automobile fuel cell or a home fuel cell, inwhich starting and stopping is necessary on daily basis, then, becausestarting from normal temperatures is requires a significant amount oftime, it becomes necessary to constantly burn hydrocarbon fuel, which isthe raw material for reforming, in order to keep the reformer near thereforming temperature.

Adopting the pre-reformer for CPO allows the reforming efficiency to beincreased, but on the other hand, the temperature of the catalyst layerinlet portion quickly becomes a high temperature, as discussed in JP2001-146406A, and thus there is the problem that hydrocarbons having twoor more carbon atoms are thermally decomposed and deposit carbon,precluding stable use of the apparatus over extended periods.

SUMMARY OF THE INVENTION

The present invention was arrived at in light of the foregoing matters,and it is a first object thereof to solve the problems of conventionalautothermal reformers with a pre-reformer by providing a reformed gasproduction method and a reformed gas production apparatus that achieve ahigh reforming efficiency while preventing a drop in catalyst activitydue to carbon deposition and maintaining stable performance overextended periods.

A second object is to provide a reformed gas production method and areformed gas production apparatus with which it is possible to shortenthe activation time.

A first characteristic means of the reformed gas production methodaccording to the invention for achieving the foregoing object is areformed gas production method of using a reforming catalyst to reform afuel that contains a hydrocarbon having at least two carbon atoms so asto produce a reformed gas that includes methane, hydrogen, and carbonmonoxide, the method comprising supplying a fluid that includes thefuel, at least one of steam and a carbon dioxide-containing gas, and anoxygen-containing gas, to a reforming reaction region, and with thethermal decomposition index temperature of the fuel, which is determinedby the type and the concentration of the hydrocarbons having at leasttwo carbon atoms that makes up the fuel, serving as an upper limittemperature of the reforming reaction region, bringing the fluid intocontact with the reforming catalyst to produce the reformed gas.

That is, according to this first characteristic means, if a fuel thatcontains hydrocarbons having two or more carbon atoms is to be reformedinto methane, hydrogen, and carbon monoxide, then in the reformingreaction region the fuel and an oxygen-containing gas are brought intocontact with the reforming catalyst to expedite the exothermic partialoxidation reaction that produces hydrogen and carbon monoxide, and atthe same time, the heat that is generated by this partial oxidationreaction is used to speed up the steam reforming reaction of reactingthe fuel with water or carbon dioxide to reform the fuel into methane,which has a single carbon atom, hydrogen, and carbon monoxide. At thistime, by setting the upper limit of the temperature in the reformingreaction region to the thermal decomposition index temperature of thefuel, it is possible to prevent thermal decomposition of the fuel, whichcontains hydrocarbons that have at least two carbon atoms. Depending onthe conditions that are chosen, it is also possible to balance the heatgenerated by the partial oxidation reaction and the heat required forthe steam reforming reaction, thereby obviating the need for the supplyof heat from the outside.

It should be noted that the fuel in the present invention corresponds tothe raw material for the reformed gas.

Here, thermal decomposition is used to mean the decomposition of ahydrocarbon into carbon or hydrogen, etc., in the gaseous phase or on asolid surface. In the present invention, the thermal decomposition indextemperature of the fuel is used to mean the lower limit temperature ofthe fuel at which this phenomenon is readily observed.

The present inventors found that the thermal decomposition temperatureat which a hydrocarbon thermally decomposes is dependant on theconcentration of that hydrocarbon. After much keen investigation, theinventors arrived at the relationship between the concentration of thehydrocarbon and its thermal decomposition temperature shown in FIG. 19through a method that will be discussed later.

Consequently, the thermal decomposition temperature of the hydrocarbonsmaking up the fuel (that is, the thermal decomposition temperature thatis determined by the type and the concentration of the hydrocarbonsmaking up the fuel) is set as the thermal decomposition indextemperature of the fuel, and by regarding this as the upper limittemperature, it is possible to prevent thermal decomposition of thefuel. That is, this temperature is set as the upper limit, and measuresare taken to prevent this temperature from being reached.

Thus, as in the present invention, the safest and most reliable methodto prevent a drop in catalyst activity due to carbon deposition andmaintain stable performance over extended periods is to perform thereforming reactions under conditions in which the temperature in thereforming reaction region does not exceed the thermal decompositionindex temperature of the fuel that is supplied. Incidentally, nodisclosure of the matter of performing autothermal reforming taking thethermal decomposition index temperature that is determined based on theconcentration of the hydrocarbon in the fuel as the upper limit of thetemperature in the reforming reaction region was found in the prior artmentioned above. For example, in JP 2000-84410A, autothermal reformingis performed under the condition of 800° C. using naphtha (includinghydrocarbons having five or more carbon atoms) as the hydrocarbon fuel,and because the reaction temperature is greater than the thermaldecomposition index temperature of naphtha, carbon is depositeddepending on the catalyst. In JP 2001-146406A, judging from the factthat the reforming reaction is carried out with the a heavy hydrocarbonserving as the fuel and a catalyst layer inlet temperature of 550° C.and a 680° C. outlet temperature, it can be assumed that the temperatureof the catalyst layer, which is the reforming reaction region, isalready a high temperature that is in excess of the thermaldecomposition index temperature of the fuel, and in fact carbondeposition was observed. In JP 2002-97479A, a fuel that includesmethane, ethane, propane, butane, and pentane is used as the hydrocarboncomponent, but judging from the fact that the outlet temperature isalready at least 705° C., it is fair to assume that the temperature ofthe reforming reaction region is an even higher temperature that is inexcess of the thermal decomposition temperature of the fuel.

Therefore, the present invention provides a reformed gas productionmethod that achieves a high reforming efficiency while preventing a dropin catalyst activity due to carbon deposition and maintaining stableperformance over an extended period.

A second characteristic means of the same is that the fuel is a mixedfuel that contains a plurality of types of hydrocarbons each having atleast two carbon atoms, and that the thermal decomposition indextemperature of the fuel is set to the value of the lowest temperature ofthe thermal decomposition temperatures found based on the concentrationin the fuel of at least two types of hydrocarbons of the hydrocarbonshaving at least two carbon atoms that make up the fuel.

That is, according to this second characteristic means, if the fuel is amixed fuel that has a plurality of types of hydrocarbons each having atleast two carbon atoms, then those thermal decomposition temperaturescorresponding to the concentrations are found from the concentrations ofthe hydrocarbons in the fuel based on the relationship between theconcentrations of the hydrocarbons and their thermal decompositiontemperatures, such as that shown in FIG. 19, and the value of the lowesttemperature of those thermal decomposition temperatures is set as thethermal decomposition index temperature of the fuel. As a result, thethermal decomposition index temperature of the fuel can be set to alower temperature than each of the thermal decomposition temperatures ofthe hydrocarbons constituting the fuel, and thus thermal decompositionof the fuel can be reliably prevented. Thus, it is possible to achieve ahigh reforming efficiency while preventing a drop in the catalystactivity due to the deposition of carbon and maintaining stableperformance over long periods of time.

Even if the fuel contains 50% or more methane, which is a hydrocarbonthat has a single carbon atom, by setting the thermal decompositionindex temperature based on the type and the concentration of thehydrocarbons that have two or more carbon atoms as discussed above it ispossible to favorably achieve the objectives of the present invention.

Natural gas can be adopted as the fuel that is used in the presentinvention. In this case, the general composition of natural gas does notinclude substantially any hydrocarbons that have six or more carbonatoms, and even if it does, the concentration of those hydrocarbons islow and they have little effect, and thus the thermal decompositiontemperatures of the hydrocarbons that have five or less carbon atomsshould be taken into consideration. That is, if natural gas is used asthe fuel, then from the concentrations of the hydrocarbons each having 2to 5 carbon atoms, of the hydrocarbons that have two or more carbonatoms, it is possible to find the thermal decomposition temperaturescorresponding to those concentrations and then to set the value of thelowest temperature of those thermal decomposition temperatures as thethermal decomposition index temperature of the fuel. For example, thelowest value of the thermal decomposition temperatures corresponding tothe respective concentrations of ethane, propane, n-butane, n-pentane,i-butane, and i-pentane, which may be contained in natural gas, can beset as the thermal decomposition index temperature of the fuel.

A third characteristic means of the same is that a supply amount ratioof at least one of the oxygen-containing gas, the steam, and the carbondioxide-containing gas that are supplied to the reforming reactionregion with respect to the fuel is changed to adjust the temperature inthe reforming reaction region.

That is, according to this third characteristic means, the temperatureof the reforming reaction region is related to the balance between theheat generated by the partial oxidation reaction and the heat consumedby the steam reforming reaction, and thus the supply amount ratio of atleast one of the oxygen-containing gas, the steam, and the carbondioxide-containing gas with respect to the fuel is adjusted such thatthe thermal decomposition index temperature of the fuel becomes theupper limit of the temperature in the reforming reaction region.

For example, when the ratio of the supply amount of theoxygen-containing gas with respect to the fuel is increased, the rate ofthe partial oxidation reaction of the hydrocarbon fuel is increased, andthus the temperature of the reforming reaction region increases, whereaswhen the ratio of the supply amount of the oxygen-containing gas withrespect to the fuel is reduced, the partial oxidation reaction of thehydrocarbon fuel is inhibited, and thus the temperature of the reformingreaction region drops. Similarly, when the ratio of the supply amount ofthe steam or the carbon dioxide-containing gas with respect to the fuelis increased, the endothermic reforming reaction of the hydrocarbon fuelis expedited, and thus the temperature of the reforming reaction regiondrops, whereas when the ratio of the supply amount of the steam or thecarbon dioxide-containing gas with respect to the fuel is reduced, theendothermic reforming reaction of the hydrocarbon fuel is inhibited, andthus the temperature of the reforming reaction region increases.

Thus, a favorable embodiment of a reformed gas production method withwhich by changing the supply amount of at least one of theoxygen-containing gas, the steam, and the carbon dioxide-containing gaswhile keeping the supply amount of the hydrocarbon fuel constant it ispossible to adjust the temperature of the reforming reaction region to asuitable temperature is provided.

A fourth characteristic means of the same is that a hydrogen-containinggas is supplied to the reforming reaction region.

That is, according to this fourth characteristic means, it is possibleto supply hydrogen-containing gas to the reforming reaction region toquickly raise the temperature of the reforming reaction region.

For example, when a hydrogen-containing gas, the fuel, and theoxygen-containing gas are supplied to the reforming reaction region,then the hydrogen, which starts to combust at a lower temperature thanthe hydrocarbon fuel, reacts with the oxygen and is combusted, andhydrogen combusts on the reforming catalyst, even in the presence ofsteam, when the temperature of the reforming reaction region is 100° C.or more, and thus the heat from combustion of the hydrogen quicklyraises the temperature of the reaction chamber without an accompanyingdeposition of carbon material, and this allows partial oxidation andsteam reforming to be run smoothly.

Thus, a favorable embodiment of a reformed gas production method withwhich a quick temperature raising operation becomes possible isprovided.

A fifth characteristic means of the same is that until the temperatureof the reforming reaction region reaches a suitable operatingtemperature necessary to reform the fuel (the temperature at which thefuel starts being reformed), the hydrogen-containing gas and anoxygen-containing gas are supplied to the reforming reaction region andthe hydrogen is combusted, and with that heat from the combustion ofhydrogen, the temperature of the reforming reaction region is raised upto the suitable operating temperature.

That is, according to this fifth characteristic means, when theapparatus is first activated, hydrogen-containing gas andoxygen-containing gas are supplied to the reforming reaction region, andwith the heat that is produced by the catalyst-mediated combustionreaction between the hydrogen and the oxygen, in a short time thetemperature of the reforming reaction region can be quickly raised to asuitable operation temperature.

Thus, a favorable embodiment of a reformed gas production method thathas superb activation properties is provided.

A sixth characteristic means of the same is that the reforming catalystis a catalyst whose primary component is a metal that has a steamreforming capability.

That is, according to this sixth characteristic means, a reformingcatalyst whose primary component is a metal that has a steam reformingcapability is provided in the reforming reaction region. A catalystwhose primary component is preferably one metal selected from Ni, Co,Ru, Rh, Pt, and Pd is favorable. Although there are no particularlimitations regarding the substrate, the substrate preferably has as itsprimary component one selected from alumina, zirconia, silica, titania,magnesia, and calcia.

Consequently, a favorable embodiment of a reformed gas production methodprovided with a reforming catalyst for favorably achieving a reformingaction in the reforming reaction region is provided.

A seventh characteristic means of the same is that before being suppliedto the reforming reaction region, at least one of the fuel, theoxygen-containing gas, the steam, and the carbon dioxide-containing gasis subjected to desulfurization.

That is, according to this seventh characteristic means, after thoroughinvestigation by the present inventors in order to clarify thecorrelation between the sulfur concentration in the fluid that issupplied to the reforming reaction region and the reforming reactionactivity and the maximum temperature in the reforming reaction region,it was found that sulfur compounds cause a sudden drop in catalyticactivity and raise in the temperature of the reforming reaction region.Thus, the fluid is supplied to the reforming reaction region aftersulfur compounds in the gases are removed. It should be noted that acopper-zinc-based desulfurizing agent whose primary components arecopper oxide CuO and zinc oxide ZnO can be adopted to effectdesulfurization.

Thus, a favorable embodiment of a reformed gas production method withwhich a drop in reforming performance due to sulfur poisoning of thereforming catalyst is substantially prevented and a drop in reformingcatalyst activity due to carbon deposition is prevented, allowing stableperformance to be maintained over an extended period of time, isprovided.

An eighth characteristic means of the same is that the entire fluid issubjected to desulfurization before being supplied to the reformingreaction region such that the concentration of sulfur compounds is notmore than 2.4 mol·ppb.

That is, according to this eighth characteristic means, the presentinventors, through a method that will be discussed later, found therelationship between the concentration of dimethyl sulfide (hereinafterabbreviated as DMS), which is a sulfur compound, in the fluid and themaximum temperature in the reforming reaction region, as shown in FIGS.11 to 13. That is, by desulfurizing the entire fluid such that theconcentration of sulfur compounds is not more than 2.4 mol·ppb beforethe fluid is supplied to the reforming reaction region, it is possibleto almost entirely eliminate the effect that sulfur compounds haveregarding the drop in reforming catalyst activity and the rise inreforming reaction region temperature. It should be noted that theconcentration of the sulfur compounds is more preferably not more than1.5 mol·ppb and even more preferably not more than 1.3 mol·ppb.

Thus, a favorable embodiment of a reformed gas production method withwhich sulfur poisoning of the reforming catalyst that is provided in thereaction chamber and a rise in the temperature of the reforming reactionregion can be reliably prevented is provided.

A ninth characteristic means of the same is that a fluid that includesan oxygen-containing gas and the reformed gas that is created in thereforming reaction region is supplied to a second reforming reactionregion and brought into contact with a second reforming catalyst, amaximum temperature in the second reforming reaction region ismaintained within a temperature range of 400 to 1200° C., and an outlettemperature of the second reforming reaction region is adjusted suchthat it is higher than an outlet temperature of the reforming reactionregion, so as to produce a second reformed gas that includes hydrogenand carbon monoxide.

That is, according to this ninth characteristic means, in the case ofreforming a fuel that contains hydrocarbons that have two or more carbonatoms into hydrogen and carbon monoxide, a two-stage structure in whichthere is an early stage reforming reaction region and a later stagesecond reforming reaction region allows, in the early stage reformingreaction region, the thermal decomposition index temperature of the fuelto be set as the upper limit of the temperature in the reformingreaction region as discussed above so as to produce methane (one carbonatom) while preventing thermal decomposition of that fuel, and, in thelater stage second reforming reaction region, if the exothermic partialoxidation reaction in which the reformed gas reacts with anoxygen-containing gas and the endothermic steam reforming reaction inwhich the reformed gas reacts with either steam or carbon dioxide arerun simultaneously, allows the temperature of the second reformingreaction region to be kept below 1200° C., which is the temperature atwhich the thermal decomposition of methane becomes noticeable, therebypreventing the thermal decomposition of methane. On the other hand, ifthe reaction temperature of the second reforming reaction region is toolow, then the reforming reaction of methane will not proceed, and thusthe lower limit temperature is set to 400° C. and the temperature of thesecond reforming reaction region is set to a temperature within therange of 400° C. to 1200° C. (not inclusive of 1200° C., however).

Further, adjusting the temperature of the second reforming reactionregion such that the outlet temperature of the second reforming reactionregion is higher than the outlet temperature of the reforming reactionregion speeds up the partial oxidation reaction in the second reformingreaction region of the reformed gas that is created in the reformingreaction region, and thus the proportion of hydrogen can be lowered, andthe proportion of carbon monoxide can be raised, in the composition ofthe reformed gas created in the second reforming reaction region.

Thus, a favorable embodiment of a reformed gas production method withwhich, in the case of reforming a fuel that contains hydrocarbons thathave two or more carbon atoms into hydrogen and carbon monoxide, in thelater stage second reforming reaction region it is possible to achieve ahigh reforming efficiency while the drop in catalyst activity due tocarbon deposition and deterioration of the catalyst due to excessiveheat are prevented, allowing stable performance to be maintained over anextended period of time, and with which it is also possible to produce afavorable reformed gas that has a low ratio of hydrogen to carbonmonoxide as the raw material of a liquid fuel, for example.

A tenth characteristic means of the same is that at least one of steamand a carbon dioxide-containing gas is supplied to the second reformingreaction region.

That is, according to this tenth characteristic means, in a case wherethe reformed gas that is created in the early stage reforming reactionregion is to be reformed into a synthesis gas that includes hydrogen andcarbon monoxide in the second reforming reaction region, the exothermicpartial oxidation reaction in which the reformed gas reacts with anoxygen-containing gas to create hydrogen and carbon monoxide is allowedto proceed, and simultaneously the heat that is generated by thispartial oxidation reaction is used to run the endothermic steamreforming reaction, in which the reformed gas reacts with either steamor carbon dioxide to create hydrogen and carbon monoxide. Depending onthe conditions that are chosen, it is also possible to balance the heatgenerated by the partial oxidation reaction and the heat required forthe steam reforming reaction, thus obviating the need for the supply ofheat from the outside. In this case, when the supply ratio between thesteam and the carbon dioxide-containing gas that are supplied to thesecond reforming reaction region is changed, the proportion of hydrogenand carbon monoxide in the synthesis gas that is created is changed.

Consequently, a favorable embodiment of a reformed gas production methodwith which, in the case of reforming a reformed gas that is made ofmethane, hydrogen, and carbon monoxide into a second reformed gas thatincludes hydrogen and carbon monoxide, it is possible to achieve a highreforming efficiency while allowing the proportion of hydrogen andcarbon monoxide in the second reformed gas that is created to beadjusted as necessary is provided.

An eleventh characteristic means of the same is that a supply amountratio of at least one of the oxygen-containing gas, the steam, and thecarbon dioxide-containing gas, which are supplied to the secondreforming reaction region, with respect to the reformed gas is changedto adjust the temperature of the second reforming reaction region.

That is, according to this eleventh characteristic means, thetemperature of the second reforming reaction region is related to thebalance between the heat produced by the partial oxidation region andthe heat consumed by the steam reforming reaction, and thus to adjustthe temperature of the second reforming reaction region, the ratio ofthe supply amount of at least one of the oxygen-containing gas, thesteam, and the carbon dioxide-containing gas with respect to thereformed gas is adjusted.

For example, when the ratio of the supply amount of theoxygen-containing gas with respect to the reduced gas is increased, therate of the partial oxidation reaction of the reduced gas is increased,and thus the temperature of the second reforming reaction regionincreases, whereas when the ratio of the supply amount of theoxygen-containing gas with respect to the reduced gas is reduced, thepartial oxidation reaction of the reduced gas is inhibited, and thus thetemperature of the second reforming reaction region drops. Similarly,when the ratio of the supply amount of the steam or the carbondioxide-containing gas with respect to the reduced gas is increased, theendothermic reforming reaction of the reduced gas is sped up, and thusthe temperature of the second reforming reaction region drops, whereaswhen the ratio of the supply amount of the steam or the carbondioxide-containing gas with respect to the reduced gas is reduced, theendothermic reforming reaction of the reduced gas is inhibited, and thusthe temperature of the second reforming reaction region increases.

Consequently, a favorable embodiment of a reformed gas production methodwith which by changing the supply amount of at least one of theoxygen-containing gas, the steam, and the carbon dioxide-containing gaswhile keeping the supply amount of the reduced gas constant it ispossible to adjust the temperature of the second reforming reactionregion to a suitable temperature is provided.

A twelfth characteristic means of the same is that, before beingsupplied to the second reforming reaction region, at least one of thereformed gas, the oxygen-containing gas, the steam, and the carbondioxide-containing gas is subjected to desulfurization.

That is, according to this twelfth characteristic means, the sulfurcompounds in the respective gases are removed before those gases atsupplied to the second reforming reaction region such that the activityof the second reforming catalyst of the second reforming reaction regiondoes not drop due to those sulfur compounds. As a specific value of asulfur compound concentration of the entire fluid at which sulfurpoisoning of the second reforming catalyst in the second reformingreaction region does not occur, it is preferable that the concentrationof sulfur compounds is set to not more than 2.4 mol·ppb for the samereasons as those given in the description of eighth characteristicmeans. It is further preferable that this concentration is set to notmore than 1.5 mol·ppb and even more preferably to not more than 1.3mol·ppb. It should be noted that a copper-zinc-based desulfurizing agentwhose primary components are copper oxide CuO and zinc oxide ZnO can beadopted to effect desulfurization.

Consequently, a favorable embodiment of a reformed gas production methodin which the reforming ability of the second reforming catalyst of thesecond reforming reaction region does not drop due to sulfur poisoningis provided, and at the same time, a favorable embodiment of a reformedgas production method with which a favorable reforming gas that does notinclude sulfur compounds can be produced as the raw material for aliquid fuel, for example, is provided.

A thirteenth characteristic means of the same is that the secondreforming catalyst is a catalyst whose primary component is a metal thathas a steam reforming capability.

That is, according to this thirteenth characteristic means, a secondreforming catalyst whose primary component is a metal that has a steamreforming capability is provided in the second reforming reactionregion. A catalyst whose primary component is preferably one metalselected from Ni, Co, Ru, Rh, Pt, and Pd is favorable. Although thereare no particular limitations regarding the substrate, the substratepreferably has as its primary component one selected from alumina,zirconia, silica, titania, magnesia, and calcia.

Thus, a favorable embodiment of a reformed gas production methodprovided with a second reforming catalyst that achieves a favorablereforming effect in the second reforming reaction region is provided.

A fourteenth characteristic means of the same is that a total gas flowamount that is supplied to the reforming reaction region is a gas-spacevelocity per hour within a range of 750 h⁻¹ to 300000 h⁻¹.

That is, according to this fourteenth characteristic means, the steamreforming reaction and the partial oxidation reaction, which has a fastrate of reaction, are run simultaneously in the reforming reactionregion, and thus the total gas flow that is supplied to the reformingreaction region can be changed over the broad range of a gas-spacevelocity per hour of 750 h⁻¹ to 300000 h⁻¹ so that the reformingreaction can be suitably carried out within the reaction chamberregardless of whether the amount of reformed gas that is created isincreased or decreased.

Thus, a favorable embodiment of a method for operating a reformed gasproduction apparatus with which it is possible to stably carry out thereforming reaction over a wide range of gas flow amounts is provided.

A first characteristic configuration of a reformed gas productionapparatus according to the present invention that is for achieving theforegoing objectives is a reformed gas production apparatus thatcomprises a reaction chamber containing a reforming catalyst, a supplyroute that supplies a fluid that includes a fuel containing ahydrocarbon having at least two carbon atoms, at least one of steam anda carbon dioxide-containing gas, and an oxygen-containing gas, to thereaction chamber, a reformed gas conduction route that conducts areformed gas that is created through a reforming reaction and thatincludes methane, hydrogen, and carbon monoxide, from the reactionchamber, and reaction chamber temperature control means that controls atemperature of the reaction chamber, wherein the fuel is a mixed fuelthat contains a plurality of types of hydrocarbons each having at leasttwo carbon atoms, and wherein the reaction chamber temperature controlmeans sets the thermal decomposition index temperature of the fuel,which is determined based on the gas type and the concentration of thehydrocarbons having at least two carbon atoms that make up the fuel, asthe upper limit temperature of the reforming reaction region, and in acase where the maximum temperature in the reforming reaction regionexceeds the upper limit temperature, the reaction chamber temperaturecontrol means performs control to cool the reaction chamber.

That is, according to this first characteristic configuration, if amixed fuel that contains hydrocarbons having two or more carbon atoms isto be reformed into methane, hydrogen, and carbon monoxide, then theexothermic partial oxidation reaction, in which the fuel and anoxygen-containing gas are reacted to produce hydrogen and carbonmonoxide, is run in the reaction chamber advance, and at the same time,the heat that is generated by this partial oxidation reaction is used topush forward the steam reforming reaction of reacting the fuel withwater or carbon dioxide to reform the fuel into methane, which has asingle carbon atom, hydrogen, and carbon monoxide, for example. At thistime, the thermal decomposition index temperature of the fuel isregarded as the upper limit temperature of the temperature in thereaction chamber and control is performed such that the temperature inthe reaction chamber is controlled does not reach this upper limittemperature, and if it does exceed the upper limit temperature, then itis possible to perform a control for cooling the reaction chamber inorder to prevent thermal decomposition of the fuel.

Thus, a reformed gas production apparatus with which a high reformingefficiency can be achieved while a drop in catalyst activity due tocarbon deposition can be prevented so that stable performance ismaintained over an extended period of time is provided.

A second characteristic configuration of the same is that the value ofthe lowest temperature of the thermal decomposition temperatures foundbased on a concentration in the fuel of at least two types ofhydrocarbons having at least two carbon atoms that make up the fuel isselected as the thermal decomposition index temperature of the fuel.

That is, according to this second characteristic configuration, thethermal decomposition temperatures corresponding to the concentrationsin the fuel of hydrocarbons that have two or more carbon atoms containedin the fuel are found, and the value of the lowest of those thermaldecomposition temperatures can be set as the thermal decomposition indextemperature of the fuel. The thermal decomposition index temperature iscontrolled such that it does not exceed this temperature, and if it doesexceed this temperature, and it is possible to perform a control to coolthe reaction chamber so that thermal decomposition of the fuel isreliably prevented. As a result, it is possible to achieve highreforming efficiency while preventing a drop in the catalyst activitydue to the deposition of carbon so as to maintain stable performanceover an extended period of time.

A third characteristic configuration of the same is that the fuelcontains at least 50% methane.

That is, according to this third characteristic configuration, even ifthe fuel contains 50% or more methane, by regarding the temperaturedetermined based on the gas type and concentration of the hydrocarbonshaving two or more carbon atoms that make up the fuel as the thermaldecomposition index temperature and performing control to keep thistemperature as the upper limit, it is possible to reliably preventthermal decomposition of the fuel.

A fourth characteristic configuration of the same is that the fuel is anatural gas, and the thermal decomposition index temperature of the fuelis set to the value of the lowest temperature of the thermaldecomposition temperatures found based on a concentration in the fuel ofhydrocarbons having from 2 to 5 carbon atoms that make up the fuel.

That is, according to this fourth characteristic configuration, naturalgas can be adopted as the fuel that is used, in which case the generalcomposition of natural gas does not include substantially anyhydrocarbons that have six or more carbon atoms, and even if it does,the concentration of those hydrocarbons is low and they have littleeffect, and thus the thermal decomposition temperatures of those arefound from the concentrations of the hydrocarbons each having 2 to 5carbon atoms, of the hydrocarbons that have two or more carbon atoms,and the value of the lowest thermal decomposition temperature of thosecan be to set as the thermal decomposition index temperature of thefuel. For example, the lowest value of the thermal decompositiontemperatures corresponding to the respective concentrations of ethane,propane, n-butane, n-pentane, i-butane, and i-pentane, which may becontained in the natural gas, can be taken as the thermal decompositionindex temperature of the fuel.

A fifth characteristic configuration of the same is that theconcentration is the hydrocarbon concentration of the fuel at an inletportion of the reaction chamber.

That is, according to this fifth characteristic configuration, thehydrocarbons in the fuel are reformed through the reforming reaction inthe reaction chamber, and as a result their concentrations drop. On theother hand, as shown in FIG. 19, the thermal decomposition temperaturesof the hydrocarbons increase as the concentrations of those hydrocarbonsdecreases. Thus, by performing control to set the thermal decompositiontemperature of the fuel based on the highest concentration of thehydrocarbons in the fuel, that is, the concentration at which thethermal decomposition temperature is lowest, thermal decomposition ofthe fuel can be reliably prevented.

A sixth characteristic configuration of the same is that a temperaturesensor that detects the temperature of the reforming reaction region,and control means that controls the temperature of the reaction chamberby adjusting a supply amount ratio of at least one of theoxygen-containing gas, the steam, and the carbon dioxide-containing gasthat are supplied to the reforming reaction region with respect to thefuel based on the information detected by the temperature sensor, areprovided as the reaction chamber temperature control means.

That is, according to this sixth characteristic configuration, the ratioof the supply amount of at least one of the oxygen-containing gas, thesteam, and the carbon dioxide-containing gas supplied into the reactionchamber with respect to the fuel is adjusted based on the detectedtemperature within the reaction chamber. It should be noted that becauseit is difficult to control the temperature when the ratio of the amountof oxygen-containing gas that is supplied with respect to the fuel(O₂/C) is too high, in large-scale apparatuses it is preferable thatthis supply amount ratio (O₂/C) is in the range of 0.01 to 0.5.

Thus, a favorable embodiment of a reformed gas production apparatus withwhich accurate automatic temperature control of the temperature withinthe reaction chamber based on the detected information on the reformingreaction region temperature within the reaction chamber is possible isprovided.

A seventh characteristic configuration of the same is that the apparatusis further provided with a temperature adjustment mechanism that iscapable of cooling or heating the reforming reaction region.

That is, according to this seventh characteristic configuration, if thetemperature of the reforming reaction region has become too high, thenthe reaction chamber is cooled so that the thermal decomposition indextemperature of the fuel is not exceeded, and if the temperature of thereforming reaction region has become too low for the reaction to proceedsmoothly, then the reaction chamber is heated. It should be noted thatthe reaction chamber is cooled and heated either by cooling and heatingthe entire reaction chamber or by lowering and raising the inlettemperature of the reaction chamber.

Thus, a favorable embodiment of a reformed gas production apparatus withwhich the reaction temperature of the reforming reaction region can bemaintained such that it does not deviate from a suitable temperaturerange is provided.

An eighth characteristic configuration of the same is that the apparatusis further provided with detection means that detects a type and aconcentration of hydrocarbons having at least two carbon atoms that makeup the fuel that is supplied to the reaction chamber, and thermaldecomposition index temperature derivation means that derives thethermal decomposition index temperature of the fuel based on the typeand the concentration of the hydrocarbons detected by the detectionmeans.

That is, with this eighth characteristic configuration, it is possibleto detect the type and concentration of the hydrocarbons and derivetheir thermal decomposition temperatures whenever fuel is supplied tothe reaction chamber, and thus the ideal thermal decomposition indextemperature can be derived even if the composition of the supplied fuelchanges, and this allows thermal decomposition of the fuel to beprevented.

Thus, a favorable embodiment of a reformed gas production apparatus withwhich the temperature in the reforming reaction region can be controlledbased on the information on the concentrations of the hydrocarbonshaving two or more carbon atoms within the supplied fuel is provided.

A ninth characteristic configuration of the same is that the apparatusis further provided with a desulfurizing apparatus that desulfurizes atleast one of the fuel, the oxygen-containing gas, the steam, and thecarbon dioxide-containing gas before it is supplied to the reactionchamber.

That is, with this ninth characteristic configuration, sulfur compoundsin the various gases are removed before those gases are supplied to thereaction chamber so that activity of the reforming catalyst contained inthe reaction chamber does not drop due to those sulfur compounds, and sothat the temperature in the reforming reaction region does not rise. Itshould be noted a copper-zinc-based desulfurizing agent whose primarycomponents are copper oxide CuO and zinc oxide ZnO can be adopted toachieve desulfurization.

Thus, a favorable embodiment of a reformed gas production apparatus withwhich a drop in the reforming ability of the reforming catalyst due tosulfur poisoning can be substantially prevented and a drop in activityof the reforming catalyst due to carbon deposition can be prevented toallow stable performance to be maintained over an extended period oftime is provided.

A tenth characteristic configuration of the same is that the apparatusfurther comprises a second reaction chamber that contains a secondreforming catalyst and that produces a second reformed gas that includeshydrogen and carbon monoxide through a second reforming reaction of thereformed gas that has been conducted from the reaction chamber, whereina maximum temperature in the second reforming reaction region of thesecond reaction chamber is maintained within a temperature range of 400to 1200° C., and an outlet temperature of the second reaction chamber isadjusted such that it is higher than an outlet temperature of thereaction chamber.

That is, according to this tenth characteristic means, in the case ofreforming a fuel that contains hydrocarbons that have two or more carbonatoms into hydrogen and carbon monoxide, a two-stage reaction chamberconfiguration in which there is an early stage reaction chamber and alater stage second reaction chamber allows, in the early stage reactionchamber, the thermal decomposition index temperature of the fuel to betaken as the upper limit of the temperature in the reforming reactionregion as discussed above to prevent thermal decomposition of the fuelwhile producing a reformed gas whose main components are methane (onecarbon atom), carbon monoxide, and hydrogen, and, in the later stagesecond reforming reaction region, if the exothermic partial oxidationreaction in which the reformed gas reacts with an oxygen-containing gasand the endothermic reforming reaction in which the reformed gas reactseither with steam or carbon dioxide are run simultaneously, allows thetemperature of the second reforming reaction region to be kept below1200° C., which is the temperature at which the thermal decomposition ofmethane noticeably occurs, to prevent the thermal decomposition ofmethane. On the other hand, when the reaction temperature of the secondreforming reaction region is too low, the reforming reaction of methanewill not proceed, and thus a lower limit temperature of 400° C. isadopted and the temperature of the second reforming reaction region isset to a temperature within the range of 400 to 1200° C. (not inclusiveof 1200° C., however).

Further, adjusting the temperature of the second reaction chamber suchthat the outlet temperature of the second reaction chamber is higherthan the outlet temperature of the reaction chamber pushes forward thepartial oxidation reaction in the second reaction chamber with respectto the reformed gas that has been created in the reaction chamber, andas a result the proportion of hydrogen in the composition of thereformed gas produced from the second reaction chamber drops, allowingthe proportion of carbon monoxide therein to be raised.

Thus, a favorable embodiment of a reformed gas production apparatus withwhich, in the case of reforming a fuel that contains hydrocarbons thathave two or more carbon atoms into hydrogen and carbon monoxide, in thelater stage second reaction chamber it is possible to achieve a highreforming efficiency while preventing a drop in catalyst activity due tocarbon deposition and deterioration of the catalyst due to excessiveheat, allowing stable performance to be maintained over an extendedperiod of time, and with which it is also possible to produce afavorable reformed gas that has a low ratio of hydrogen to carbonmonoxide as the raw material of a liquid fuel, for example, is provided.

An eleventh characteristic configuration of the same is that thereformed gas production apparatus is employed in mobile and stationaryapplications alike.

That is, according to this eleventh characteristic means, simultaneouslyrunning the partial oxidation reaction and the steam reforming reactionin the reaction chamber or the second reaction chamber allows an overallcompact reformed gas production apparatus to be formed while alsoallowing the rate of reaction to be increased in order to produce alarge amount of reformed gas, such as hydrogen. In the case of a compactreformed gas production apparatus for a mobile or a stationaryapplication, the heat that is recovered by a heat exchanger, forexample, from the high-temperature reformed gas that is created in thesecond reaction chamber can be used to heat water and thus steam thatcan be supplied to the reaction chamber or the second reaction chambercan be produced easily, and thus a special heat source for steamgeneration is not necessary, and in this regard as well, the apparatuscan be provided compact.

Thus, a favorable embodiment of a reformed gas production apparatus thatis compact and high-performance, and further that is suited for use inmobile and stationary applications, is provided.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a conceptual view of a reformed gas production apparatusaccording to the present invention;

FIG. 2 is a graph showing the configuration and the temperaturedistribution of the reformer of the reformed gas production apparatusaccording to the present invention;

FIG. 3 is a structural diagram of the testing apparatus for evaluatingthe characteristics of the low-temperature reformer;

FIG. 4 is a graph showing the results of the rise in temperature due tohydrogen combustion in the low-temperature reformer (Working Example 1);

FIG. 5 is a diagram showing the results of the experiment in whichpropane is reformed with a ruthenium-based catalyst (Working Example 2);

FIG. 6 is a diagram showing the conditions and the results of anexperiment in which propane is reformed with a nickel-based catalyst(Working Example 3);

FIG. 7 is a diagram showing the conditions and the results ofexperiments in which a pseudo-natural gas is reformed with aruthenium-based catalyst (Working Examples 4 and 5);

FIG. 8 is a diagram showing the carbon production conditions of WorkingExamples 6-1 to 6-9 and Comparative Examples 6-1 to 6-5;

FIG. 9 is a structural diagram of a testing apparatus for evaluating theproperties of a two-stage structure reformer made of a low-temperaturereformer and a high-temperature reformer;

FIG. 10 is a diagram showing the conditions and the results of anexperiment for evaluating the properties of a two-stage structurereformer made of a low-temperature reformer and a high-temperaturereformer (Working Example 7);

FIG. 11 is a diagram that shows the conditions and the results ofexperiments in which a pseudo-natural gas that includes sulfur isreformed with a ruthenium-based catalyst (Working Examples 8 through12);

FIG. 12 is a diagram that shows the conditions and the results ofexperiments in which a pseudo-natural gas that includes sulfur isreformed with a ruthenium-based catalyst (Working Examples 13 through17);

FIG. 13 is a graph showing the relationship between DMS concentrationand the catalyst layer maximum temperature;

FIG. 14 is a block diagram showing the temperature control structure ofthe low-temperature reformer according to a separate embodiment of thepresent invention;

FIG. 15 is a block diagram showing the temperature control structure ofthe low-temperature reformer according to yet another separateembodiment of the present invention;

FIG. 16 is a diagram showing the temperature adjustment mechanism of areformed gas production apparatus according to a separate embodiment ofthe present invention;

FIG. 17 is a graph showing the structure and the temperaturedistribution of a conventional partial oxidation reformer;

FIG. 18 is a graph of the structure and the temperature distribution ofa conventional partial oxidation reforming apparatus with pre-reformer;and

FIG. 19 is a graph showing the relationship between the concentration ofthe hydrocarbons and the thermal decomposition temperature.

DETAILED DESCRIPTION OF THE INVENTION

Embodiments of the reformed gas production method and the reformed gasproduction apparatus (hereinafter referred to as fuel reformingapparatus) according to the present invention are described.

FIG. 1 is a conceptual view of the fuel reforming apparatus, which ismade of two stages of reforming portions, these being a low-temperaturereforming portion 1 and a high-temperature reforming portion 2. That is,the low-temperature reforming portion 1 (hereinafter, called thelow-temperature reformer 1) of the first stage supplies a fluid thatincludes at least one of steam and a carbon dioxide-containing gas, afuel that contains hydrocarbons having two or more carbon atoms(hereinafter, this may also be referred to as hydrocarbon fuel havingtwo or more carbon atoms), and an oxygen-containing gas to a reactionchamber containing a reforming catalyst, and with the thermaldecomposition index temperature of the fuel serving as the upper limittemperature of the reforming reaction region, adjusting the temperatureof the reaction chamber in order to produce a reformed gas that includesmethane, hydrogen and carbon monoxide (hereinafter, this is referred toas the first reformed gas).

The high-temperature reforming portion 2 (hereinafter, high-temperaturereformer 2) of the later stage supplies a fluid containing theoxygen-containing gas and the first reformed gas that is produced in thereaction chamber to a second reaction chamber that contains a secondreforming catalyst, maintains the maximum temperature in the secondreformation reaction region within a temperature range of 400 to 1200°C., and adjusts the temperature of the second reaction chamber such thatthe outlet temperature of the second reforming reaction region is higherthan the outlet temperature of the reforming reaction region so as toproduce a second reformed gas that includes hydrogen and carbonmonoxide. The first reformed gas and the oxygen-containing gas aresupplied to the second reaction chamber, to which at least one of steamand a carbon dioxide-containing gas can be supplied.

As shown in FIG. 1, the fuel, the oxygen-containing gas, and the carbondioxide-containing gas that are supplied into the reaction chamber ofthe low-temperature reformer 1 are desulfurized by the desulfurizingapparatuses 3A, 3B, 3C, which are provided before the low-temperaturereformer 1. Ion-exchange water is used as the raw material to create thesteam, and therefore the steam also is desulfurized to a sulfurconcentration of a low ppb level.

The desurfurizing apparatus 3B for the oxygen-containing gas also servesas the desurfurizing apparatus for the oxygen-containing gas that issupplied to the high-temperature reformer 2, the desurfurizing apparatus3C for the carbon dioxide-containing gas also serves as thedesurfurizing apparatus for the carbon dioxide-containing gas that issupplied to the high-temperature reformer 2, and the desulfurized steamis supplied to the high-temperature reformer 2. That is, theoxygen-containing gas and the carbon dioxide-containing gas that aresupplied into the second reaction chamber of the high-temperaturereformer 2 are desulfurized by the desulfurizing apparatuses 3B and 3C,which are provided before the second reaction chamber of thehigh-temperature reformer 2.

It should be noted that it is only necessary that the amount of sulfurin the fluid is lowered to at least a desired value, and thus it is notessential for desulfurization to be performed for all of the pluralityof supplied fluids.

As shown in FIG. 2, in the fuel reforming apparatus, the low-temperaturereformer 1 is operated regarding the thermal decomposition indextemperature of the fuel as its upper limit, and the high-temperaturereformer 2 is operated within a temperature range of 400 to 1200° C.(preferably 500 to 1100° C. and more preferably 600 to 1000° C.). Forexample, if gasoline is supplied as the hydrocarbon fuel, then thetemperature in the reforming reaction region within the reaction chamberof the low-temperature reformer 1 is maintained at a temperature that isbelow the minimum thermal decomposition temperature of the hydrocarboncomponents of the gasoline that has been determined based on theconcentration of those components, and the reaction temperature withinthe second reaction chamber of the high-temperature reformer 2 ismaintained at a temperature below the thermal decomposition temperatureof methane (1200° C.). That is, the temperature is not permitted toreach or exceed 1200° C., which is the temperature at which the thermaldecomposition of methane within the first reforming gas noticeablyoccurs.

The temperature of the reaction chamber of the low-temperature reformer1 can be adjusted by changing the ratio of the supply amount at leastone of the oxygen-containing gas, the steam, and the carbondioxide-containing gas that are supplied into the reaction chamber ofthe low-temperature reformer 1 with respect to the hydrocarbon fuel.Specifically, adjusting the temperature of the reaction chamber of thelow-temperature reformer 1 is achieved by changing the ratio of theamount of oxygen-containing gas that is supplied with respect to thehydrocarbon fuel supplied to the low-temperature reformer 1.

It is also possible to supply a hydrogen-containing gas into thereaction chamber of the low-temperature reformer 1. It should be notedthat it is possible to use the offgas of a fuel cell or the reformedgas, for example, as the hydrogen-containing gas that is supplied to thelow-temperature reformer 1. There is no particular limitations regardingthe hydrogen concentration, although preferably the gas contains atleast 30% hydrogen. Also, as shown in FIG. 1, a desulfurizing apparatus3D for the hydrogen-containing gas that is supplied to thelow-temperature reformer 1 is provided before the low-temperaturereformer 1.

The reforming catalyst contained in the reaction chamber of thelow-temperature reformer 1 is a catalyst whose primary component is ametal that has the ability to reform steam. Similarly, the secondreforming catalyst contained in the second reaction chamber of thehigh-temperature reformer 2 is a catalyst whose primary component is ametal that has the ability to reform steam. The reforming catalyst andthe second reforming catalyst preferably are reforming catalysts thathave an excellent ability to reform steam and that are high resistant tocarbon deposition. Specifically, it is preferable that a precious metalcatalyst such as rhodium, iridium, platinum, palladium, or ruthenium isused, although it is also possible to use a nickel-based or acobalt-based catalyst. It is possible to use only a single type ofmetal, and as necessary it is also possible to use two or more types ofmetals together. These catalysts can have any shape, and there are noparticular limitations regarding the substrate, although preferably thesubstrate has as its main component one species selected from alumina,zirconia, silica, titania, magnesia, and calcia as, and preferably thecatalyst is used supported on the substrate in the form of atablet-shaped, spherical, or annular molding, or used molded into ahoneycomb shape.

A representative example of the manufacture of this type of catalyst isdescribed with regard to a case in which ruthenium is supported on analumina substrate. It is prepared by immersing a spherical aluminasubstrate (4 to 6 mm) in ruthenium chloride aqueous solution(RuCl₃.3H₂O) and drying it in air for two hours at 80° C., then thesubstrate is immobilized (treated with NaOH aqueous solution), reduced(treated with hydrazine aqueous solution), and then washed (treated at90° C.) and dried (left in air at 80° C.).

The total gas flow supplied to the reaction chamber of thelow-temperature reformer 1 is a gas-space velocity per hour (standardcondition converted values) within a range of 750 h⁻¹ to 300000 h⁻¹(preferably 10000 h⁻¹ to 300000 h⁻¹, more preferably 50000 h⁻¹ to 300000h⁻¹). That is, it is possible to alter the total gas flow over thisbroad range of gas-space velocities.

There is no particular limitation regarding the pressure duringreaction. Depending on the application, the reaction pressure can bechanged. For example, if the apparatus is used to produce hydrogen for afuel cell, then it will be used at near standard pressure (for example,1 MPa or less), and if it is used in a liquid fuel synthesis applicationsuch as GTL, then it can be used at about 2 to 7 MPa.

When the fuel reforming apparatus is activated, until the temperature(reaction temperature) of the reaction chamber of the low-temperaturereformer 1 reaches a suitable operating temperature (400° C., forexample) that is necessary in order to reform the hydrocarbon fuel, thehydrocarbon fuel, the hydrogen-containing gas, and the oxygen-containinggas are supplied to the reaction chamber of the low-temperature reformer1 and the hydrogen is combusted, and the heat from this combustion ofhydrogen raises the temperature of the reaction chamber of thelow-temperature reformer 1 up to that suitable operating temperature. Itshould be noted that steam also is added at some point while thetemperature is rising up to the suitable operating temperature (forexample, when the reaction temperature has reached 300° C.), andhydrogen combustion is continued in the presence of that steam. Once thetemperature of the reaction chamber of the low-temperature reformer 1has reached the suitable operating temperature, the supply of thehydrogen-containing gas into the reaction chamber of the low-temperaturereformer 1 is stopped and an operation is performed to switch to a statein which hydrocarbon fuel, oxygen-containing gas, and steam aresupplied.

It should be noted that when the apparatus is activated as above, it ispossible to supply the hydrocarbon fuel, the hydrogen-containing gas,and the oxygen-containing gas to the reaction chamber of thelow-temperature reformer 1, but when the apparatus is activated it isalso possible to supply only hydrogen-containing gas andoxygen-containing gas. Also, as the temperature is rising up to thesuitable operating temperature, it is possible to supply additionalcarbon dioxide in place of the steam, to supply additional steam andcarbon dioxide, or to not supply either steam or carbon dioxide whilethe temperature is rising up to the suitable operating temperature.

A working example of temperature decomposition temperature measurementat various concentrations of hydrocarbon is described below.

Measurement of the Thermal Decomposition Temperature

The thermal decomposition temperature was measured for five differenthydrocarbons: ethane, propane, n-butane, n-pentane, i-butane, andi-pentane.

For pure hydrocarbons (100%), the reagent gas (a hydrocarbon-heliumbased gas of a predetermined concentration) is passed at a predeterminedflow rate into a silica glass tube that is arranged passing into anelectric furnace, and after carbon deposited onto the surface of an ironsheet for carbon deposition that is arranged in a central portion of thesilica tube, the presence of carbon deposition was assed using Ramananalysis (crystalline carbon peak of 1,600 cm-1) of the carbondeposition portion surface. The present inventors call this measuringtechnique “flow measurement.”

In a case where there are gas concentrations, a TG-40 thermobalance madeby Shimazu Seisakusho was used to measure the thermal decompositiontemperature. Measurements were made primarily for the case of a 1%concentration, and for i-pentane, the case of less than 1% concentrationalso was measured. Measurement was performed in accordance with a knownmethod for measuring thermal decomposition temperature using athermobalance. That is, a high-purity (99.99% purity) thin iron film iscut into approximately 20×10 mm pieces and these are placed within aplatinum receptacle of the thermobalance and then reduced at atemperature from room temperature to 1000° C. by hydrogen gas diluted byhelium to 3%. Next, the hydrocarbon gas to be measured was passed from ahigh-pressure gas cylinder through a flowmeter into the thermobalancemeasurement apparatus while the increase in mass that follows fromcarbon deposition is measured within a temperature range of roomtemperature to 1000° C., and the temperature at which an increase inmass began to occur was regarded as the thermal decompositiontemperature.

At a result, it was found that hydrocarbon concentration and thermaldecomposition temperature have the relationship shown in FIG. 19. For100% concentration samples, the thermal decomposition temperatures ofthe various components shown in FIG. 19 are near the known thermaldecomposition temperature for that particular gas, and are representedwell. On the other hand, as can be understood from the results fori-pentane, whose concentration was found at three points, the thermaldecomposition temperature rises as the concentration drops.

The results of reforming experiments performed using the experimentalapparatus shown in FIG. 3 are described below as working examples ofexperiments performed with the low-temperature reformer 1.

The experimental apparatus is provided with a reactor 4 having areaction chamber 4A that is filled with a reforming catalyst(hereinafter, called the microreactor), a temperature recorder 5 thatmeasures and records the temperature within the microreactor 4A, a watercondenser 6 that condenses water in the output gas from the reactor 4,an automatic sampler 7 that samples the output gas that has passedthrough the water condenser 6, and a gas chromatograph 8 that analysesthe sample gas, and the supply sources for the hydrocarbon fuel gas,oxygen or air as oxygen-containing gas, hydrogen as hydrogen-containinggas, steam, carbon dioxide as carbon dioxide-containing gas, and methanecontaining a 10 ppm concentration of dimethyl sulfide (DMS) are suppliedto the catalyst-filled layer of the reaction chamber 4A after passingthrough stop valves V1 to V6. The catalyst-filled layer of the reactionchamber 4A is surrounded by the electric furnace 4B, a Raschig ring isprovided at its inlet side and silica wool is provided at its outletside.

That is, the reaction chamber 4A corresponds to the reaction chamber ofthe low-temperature reformer 1, and the temperature of the reactionchamber 4A can be adjusted by the electric furnace 4B, which serves as atemperature adjustment mechanism that is capable of heating the reactionchamber 4A. The temperature recorder 5 allows the temperature of thefluid that is supplied into the reaction chamber 4A and comes intocontact with the reforming catalyst to be measured. It should be notedthat in the following working examples the stop valves V1 to V6 aremanually operated to adjust the amount of the gases and steam that issupplied, and in all cases the reactions were performed at standardpressure.

Working Example 1 Activation of the Reforming Apparatus when the FuelGas is Propane

The characteristics of the rise in temperature due to the catalyticcombustion of hydrogen were measured to asses the activation state. Themicroreactor 4A was filled with 33 mL of a ruthenium-based reformingcatalyst Ru/Al₂O₃ (2 wt % Ru/alumina substrate, particle diameter: 0.5to 1.0 mm). The other conditions were: propane (C₃H₈) supply rate 176mL/min, hydrogen supply rate 158 mL/min, and oxygen supply rate 79mL/min. When the mixed gas of hydrogen, oxygen, and propane wasintroduced at room temperature into the reactor 4 under theseconditions, the catalyst-mediated hydrogen combustion reaction heatedthe catalyst-filled layer, raising its temperature. FIG. 4 shows thecharacteristics of the rise in the temperature of the catalyst-filledlayer inlet at this time, and after approximately 40 minutes it hadreached 400° C. (suitable operating temperature).

It should be noted that during this operation, the temperature of theelectric furnace 4B surrounding the catalyst layer was heated to atemperature 5° C. lower than the catalyst layer temperature to preventthe radiation of heat from the reactor 4 (unless this is done, thetemperatures of the reactor 4 and the catalyst layer will not rise).

Working Example 2 Reforming Propane with a Ruthenium-Based Catalyst

The partial oxidation and steam reforming reactions of propane gas wereperformed using the same apparatus as that of Working Example 1. In thisexperiment, air was used as the oxygen-containing gas.

The experiment conditions were as follows.

catalyst ruthenium supported on alumina catalyst fill amount 3.3 mL fillheight 1.0 cm reaction gas propane + air + steam O₂/C (mole ratio) 0.3to 1.4 S/C 2.5 SV 10000 h⁻¹ inlet temperature 300° C.

FIG. 5 shows the experiment results when, at SV=10000 h⁻¹ and a Tin of300° C., the O₂/C ratio is altered over a range of 0.3 to 1.4 and S/C ischanged to 2.5.

The results of the experiment indicate the following.

The greater the O₂/C ratio, the higher the maximum temperature Tmaxwithin the catalyst layer, which is the reforming reaction region, andthe catalyst layer outlet temperature Tout are with respect to the inlettemperature Tin. As a result, it was clear that it is possible tocontrol the reaction temperature with the O₂/C ratio.

It is also shown that the maximum temperature Tmax of the catalyst layeris below the thermal decomposition index temperature of propane(approximately 640° C.). That is, in this working example, the maximumtemperature Tmax of the catalyst layer was 50 to 200° C. (50, 100, 130,150, 200° C.) lower than the thermal decomposition index temperature ofpropane.

After reacting for five hours, the reactor was returned to roomtemperature, dismantled and examined. In none of the cases was it foundthat carbon deposition had occurred inside the reactor or on thecatalyst surface.

Working Example 3 Reforming Propane with a Nickel-Based Catalyst

Using a nickel catalyst Ni/Al₂O₃ (nickel concentration 22 wt %, aluminasubstrate) in lieu of a ruthenium-based catalyst, propane gas wassubjected to partial oxidation and steam reforming using the sameapparatus as that of Working Example 1. The experiment conditions andresults are shown in FIG. 6. It is clear that propane gas is stablyreformed into hydrogen and methane, for example.

It should be noted that after being loaded into the microreactor, the Nicatalyst was reduced for one hour at 400° C. by nitrogen gas thatincluded 10% hydrogen.

After the reaction, the reactor was returned to room temperature,dismantled and examined, and carbon deposition was not found to haveoccurred inside the reactor or on the catalyst surface.

Working Example 4 Reforming Pseudo-Natural Gas with a Ruthenium-BasedCatalyst

Using the same experiment apparatus as that of Working Example 1, 2.4 mLof the ruthenium-based catalyst Ru/Al₂O₃ (2 wt % Ru/alumina substrate,particle diameter: 0.5 to 1.0 mm) were filled into the microreactor 4Aand the partial oxidation and steam reforming reactions were run using apseudo-natural gas (methane concentration 88%, ethane 6%, propane 4%,i-butane 2%). In this working example, pure oxygen was used as theoxygen-containing gas. FIG. 7 shows the experiment conditions and theexperiment results.

The maximum temperature Tmax of the catalyst layer, which is thereforming reaction region, is 505° C., and the thermal decompositionindex temperature of the pseudo-natural gas is approximately 777° C.,which is the lowest temperature of thermal decomposition temperaturesfor 6% ethane, 4% propane, and 2% i-butane from FIG. 19, and thusclearly the maximum temperature Tmax is lower than this thermaldecomposition index temperature. That is, in this working example, themaximum temperature Tmax of the catalyst layer was 300° C. below thethermal decomposition index temperature of the pseudo-natural gas.

After the reaction, the reactor was returned to room temperature,dismantled and examined, and carbon deposition was not found to haveoccurred inside the reactor or on the catalyst surface.

Working Example 5 Reforming Pseudo-Natural Gas with a Ruthenium-BasedCatalyst

Using the same experiment apparatus as that of Working Example 1, 2.4 mLof the ruthenium-based catalyst Ru/Al₂O₃ (2 wt % Ru/alumina substrate,particle diameter: 0.5 to 1.0 mm) were filled into the microreactor 4Aand partial oxidation, steam reforming, and CO₂ reforming were run usinga pseudo-natural gas (methane concentration 88%, ethane 6%, propane 4%,i-butane 2%). In this working example, pure oxygen was used as theoxygen-containing gas. FIG. 7 shows the experiment conditions and theexperiment results.

It is clear that the addition of carbon dioxide allowed the H₂/CO ratioto be reduced over that of Working Example 4. The maximum temperatureTmax of the catalyst layer of the reforming reaction region is 504° C.,and clearly is lower than the approximately 777° C. thermaldecomposition index temperature of the pseudo-natural gas. That is, inthis working example, the maximum temperature Tmax of the catalyst layerwas 300° C. below the thermal decomposition index temperature of thepseudo-natural gas.

After the reaction, the reactor was returned to room temperature,dismantled and examined, and carbon deposition was not found to haveoccurred inside the reactor or on the catalyst surface.

Working Examples 6-1 to 6-9 Comparative Examples 6-1 to 6-5

Using the same experiment apparatus as that of Working Example 1, thecatalyst was filled into the microreactor 4A and partial oxidation,steam reforming, and CO₂ reforming were performed using a pseudo-naturalgas (methane concentration 88%, ethane 6%, propane 4%, i-butane 2%). Inthese working examples, pure oxygen was used as the oxygen-containinggas. FIG. 8 shows the experiment conditions and the experiment results.

It is clear from FIG. 8 that when Rh is used as the catalyst and thereactions are performed under temperature conditions in which thethermal decomposition index temperature (approximately 777° C.) servesas the upper limit temperature, the carbon deposition amount can besignificantly inhibited to less than 0.1 wt %. That is, in these workingexamples, the maximum temperature Tmax of the catalyst layer was 40 to80° C. (40, 50, 60, 70, 80° C.) below the thermal decomposition indextemperature of the pseudo-natural gas.

Also, when Pt or Pd was used as the catalyst, performing the reactionsbelow the thermal decomposition index temperature resulted in asignificant reduction in the carbon deposition amount compared to whenthose reactions were run under temperature conditions in excess of thethermal decomposition index temperature. From these results it is can beunderstood that with the reformed gas production method of the presentinvention, in which reactions are performed below the thermaldecomposition index temperature, it is possible to inhibit carbondeposition and significantly increase the durability of the catalyst.

In the above Working Examples 1 to 6, the reforming experiments wereperformed with only the early stage reforming portion (low-temperaturereformer 1). Working Example 7 below describes the results of areforming experiment in which reforming is performed in both the earlystage reforming portion (low-temperature reformer 1) and the later stagereforming portion (high-temperature reformer 2).

Working Example 7 Reforming Pseudo-Natural Gas with a Ruthenium-BasedCatalyst

Using an experimental apparatus that has two stages of microreactors inseries as shown in FIG. 9, 2.9 mL of a ruthenium-based reformingcatalyst Ru/Al₂O₃ (2 wt % Ru/alumina substrate, particle diameter: 0.5to 1.0 mm) were filled into the early stage microreactor 4A, and 2.9 mLof the same ruthenium-based reforming catalyst Ru/Al₂O₃ were filled intothe later stage microreactor 9A as a second reforming catalyst, and thenpartial oxidation, steam reforming, and CO₂ reforming were performedusing a pseudo-natural gas (methane concentration 88%, ethane 6%,propane 4%, i-butane 2%). It should be noted that the later stagereactor 9 has the same configuration as the early stage reactor 4 (seeFIG. 3), and is constituted by a microreactor 9A and an electric furnace9B, for example. It is also provided with a temperature recorder 10 formeasuring the temperature within the microreactor 9A. In Working Example7, pure oxygen was used as the oxygen-containing gas. The output gasfrom the later stage reactor 9 was sampled and analyzed.

That is, the microreactor 9A corresponds to the second reaction chamberof the high-temperature reformer 2, and the temperature of the secondreaction chamber 9A can be adjusted by the electric furnace 9B, whichserves as a temperature adjustment mechanism that is capable of heatingthe second reaction chamber 9A. The temperature recorder 10 allows thetemperature of the fluid that is supplied into the second reactionchamber 9A and comes into contact with the second reforming catalyst tobe measured.

FIG. 10 shows the experiment conditions and the experiment results. Theconditions of the early stage microreactor 4A are those shown in FIG.10, and as shown in FIG. 9, oxygen, steam, and carbon dioxide are addedvia stop valves V7 to V9 between the early stage microreactor 4A and thelater stage microreactor 9A. The total amount of steam that is added tothe inlets of the microreactors 4A and 9A with respect to thepseudo-natural gas that is introduced to the microreactor 4A inlet isrecorded under the microreactor 4A+9A conditions as the S/C ratio.Similarly, for the oxygen and the carbon dioxide, the total amount ofoxygen or carbon dioxide that is added to the inlets of themicroreactors 4A and 9A with respect to the pseudo-natural gas that isintroduced to the microreactor 4A inlet is recorded under themicroreactor 4A+9A conditions as the O₂/C ratio or the CO₂/C ratio,respectively.

The catalyst layer maximum temperature of the first stage reformer(microreactor 4A) is 512° C. and the catalyst layer maximum temperatureof the second stage reformer (microreactor 9A) is 895° C., and it waspossible to stably operate the apparatus for 200 hours. From this it canbe understood that the temperature of the second reaction chamber(microreactor 9A) is adjusted such that the outlet temperature of thesecond reaction chamber (microreactor 9A) is higher than the outlettemperature of the reaction chamber (microreactor 4A).

The maximum temperature Tmax of the early stage reforming catalyst layeris 512° C. and therefore lower in temperature than the approximately777° C. thermal decomposition index temperature of the pseudo-naturalgas. The maximum temperature Tmax of the later stage second reformingcatalyst layer is 895° C., which is a temperature that is lower than thethermal decomposition temperature of methane. That is, in this workingexample, the maximum temperature Tmax of the early stage reformingcatalyst layer is 250° C. lower than the thermal decomposition indextemperature of the pseudo-natural gas, and the maximum temperature Tmaxof the later stage reforming catalyst layer is 300° C. lower than thethermal decomposition index temperature of methane. The outlettemperature Tout of the second reforming catalyst layer of the laterstage is 843° C., which is higher than the 500° C. outlet temperatureTout of the reforming catalyst layer of the early stage. After thereaction, the reactors were returned to room temperature, dismantled andexamined, and carbon deposition was not found to have occurred insidethe reactor or on the catalyst surface of either the microreactor 4A orthe microreactor 9A.

Next, discussion will return to the results of reforming experimentsperformed using the early stage reforming portion (low-temperaturereformer 1).

Working Examples 8 to 12 Experiments in which Pseudo-Natural GasContaining Sulfur is Reformed with a Ruthenium-Based Catalyst

Using the same experiment apparatus as that of Working Example 1, 2.4 mLof a ruthenium-based reforming catalyst Ru/Al₂O₃ (2 wt % Ru/aluminasubstrate, particle diameter: 0.5 to 1.0 mm) were filled into themicroreactor 4A, the partial oxidation reaction and the steam reformingreaction were run using a pseudo-natural gas (methane concentration 88%,ethane 6%, propane 4%, butane 2%), and the reform rate (%) was found. Inthese working examples, pure oxygen was used as the oxygen-containinggas. FIG. 11 shows the experiment conditions and the experiment results.In Working Examples 8 to 12, the reactions are run under DMSconcentrations ranging up to 5 mol·ppb, where in Working Example 8 noDMS is added, in Working Example 9 the DMS concentration is 0.9 mol·ppbper total gas, in Working Example 10 the DMS concentration is 1.3mol·ppb per total gas, in Working Example 11 the DMS concentration is2.4 mol·ppb per total gas, and in Working Example 12 the DMSconcentration is 4.8 mol·ppb per total gas.

It should be noted that the reform rate in FIG. 11 is found by thefollowing expression, and expresses the proportion of carbon in the rawmaterial gas that does not remain as hydrocarbon in the output gas andis converted in CO and CO₂ gas.Reform Rate (%)=(outlet CO concentration+outlet CO₂concentration)×100/(outlet methane concentration+outlet COconcentration+outlet CO₂ concentration+outlet C2 componentconcentration×2+outlet C3 component concentration×3+outlet C4 componentconcentration×4)  [Ex. 1]

As shown in FIG. 11, no sudden drops in activity (drop in reform rate)are seen at any of the DMS concentrations under 5 mol·ppb, butparticularly below 1.3 mol·ppb it is clear that there is no effectwhatsoever (the reform rate does not change). In the case of 2.4mol·ppb, there is a slight change in reform rate over time compared toWorking Examples 8 to 10, but it is clear that in practical terms thischange is so minor enough that it has substantially no effect.Consequently, the fuel reforming apparatus is operated in such a mannerthat the sulfur concentration in the total gas supplied to the earlystage reforming portion (low-temperature reformer 1) does not exceed 2.4mol·ppb. It should be noted that these results can be similarly appliedto the later stage reforming portion (high-temperature reformer 2) aswell, and thus the fuel reforming apparatus is operated in such a mannerthat the sulfur concentration in the total gas supplied to the laterstage reforming portion (high-temperature reformer 2) does not exceed2.4 mol·ppb. Also, the maximum temperature Tmax of the catalyst layer isfrom 504° C. to 507° C., which is below the thermal decomposition indextemperature of the pseudo-natural gas (approximately 777° C.). That is,in these working examples, the maximum temperature Tmax of the catalystlayer is 250° C. lower than the thermal decomposition index temperatureof the pseudo-natural gas.

After the reactions, the reactors were returned to room temperature,dismantled and examined, and carbon deposition was not found to haveoccurred inside the reactor or on the catalyst surface in any of theworking examples.

Working Examples 13 to 17

Using the same experiment apparatus as that of Working Example 1, 300 mLof a ruthenium-based reforming catalyst Ru/Al₂O₃ (2 wt % Ru/aluminasubstrate, particle diameter: 0.5 to 1.0 mm) were filled into themicroreactor 4A and partial oxidation and steam reforming were run usinga pseudo-natural gas (methane concentration 88%, ethane 6%, propane 4%,butane 2%). In these working examples, pure oxygen was used as theoxygen-containing gas. The experiment conditions and the experimentresults are shown in FIG. 12 and FIG. 13. The sulfur concentrations,catalyst quantity, and O₂/C ratios are different from those of WorkingExamples 8 to 12. That is, in Working Examples 13 to 17 the reactionsare performed over DMS concentrations ranging up to 50.5 mol·ppb, wherein Working Example 13 the DMS concentration is 0.5 mol·ppb per totalgas, in Working Example 14 the DMS concentration is 1.5 mol·ppb pertotal gas, in Working Example 15 the DMS concentration is 5.5 mol·ppbper total gas, in Working Example 16 the DMS concentration is 10.5mol·ppb per total gas, and in Working Example 17 the DMS concentrationis 50.5 mol·ppb per total gas. Also, the amount of catalyst was set to125 times the amount of catalyst in Working Examples 8 to 12, and theO₂/C ratio was set to 0.2.

As shown in FIG. 12 and FIG. 13, in these working examples, the amountof catalyst is greater and the O₂/C ratio is larger than in WorkingExamples 8 to 12, resulting in an overall higher catalyst layer maximumtemperature, however, the reactions were run at temperatures below thethermal decomposition index temperature of the pseudo-natural gas(approximately 777° C.) at all DMS concentrations. Also, there is atrend toward higher catalyst layer maximum temperatures the higher theDMS concentration, and in particular, it was found that the catalystlayer maximum temperature jumps sharply when the DMS concentration isgreater than 2.4 mol·ppb. Consequently, it was found that to carry outthe reactions at lower catalyst layer maximum temperatures, it ispreferable that the DMS concentration is low, particularly preferably ator less than 2.4 mol·ppb and even more preferably at or less than 1.5mol·ppb.

It should be noted that in these working examples, the maximumtemperature Tmax of the catalyst layer ranged from 700° C. to 762° C.,which is 15 to 80° C. (15, 50, 80° C.) below the thermal decompositionindex temperature of the pseudo-natural gas (approximately 777° C.).

The above Working Examples 1 to 17 and the Comparative Example 6 wereperformed at standard pressure using an experiment apparatus shown inFIG. 3 of FIG. 9. Consequently, when the heat-resistance properties ofthe reactors 4 and 9 or the reaction pressure is changed, there is thepossibility that the maximum temperature Tmax of the catalyst layer orthe output gas composition will change, even if the other conditions areidentical to those of the Working Examples 1 to 17 or the ComparativeExample 6. However, in this case it is possible to still keep themaximum temperature Tmax of the catalyst layer below the thermaldecomposition temperature of the hydrocarbon raw material by changing atleast one of the S/C ratio, the O₂/C ratio, and the CO₂/C ratio in theinlet gas or by heating or cooling from the outside.

As described above, the fuel reforming apparatus according to theinvention can be used under large gas-space velocity conditions and canbe made compact, and thus is suited for use in a mobile member such asan automobile (for installation in a mobile member) or for stationaryuse (for a stationary compact power source, for example). As for anapplication in which it is mounted in a mobile member, it can be used tosupply hydrogen fuel to a fuel cell that functions as an automobilepower system, and one example where it can be used in a stationarycompact power source is to supply hydrogen fuel to a fuel cell that isused to generate power in a small office, for example.

Other Embodiments

Other embodiments of a method for operating the reformed gas productionapparatus according to the present invention are described below.

In the foregoing embodiment, the reformed gas production apparatus (fuelreforming apparatus) has a two-stage structure constituted by a earlystage low-temperature reforming portion 1 (reaction chamber) and a laterstage high-temperature reforming portion 2 (second reaction chamber),but it is also possible to adopt a configuration in which it is providedwith only the early stage low-temperature reforming portion 1 (reactionchamber).

In the foregoing embodiment, the temperature of the experimentalreaction chamber 4A of the reactor 4, which corresponds to the reactionchamber of the low-temperature reforming portion 1, is measured (seeFIG. 3), and the O₂/C ratio is changed manually while watching theresults of that measurement (that is, the amount of oxygen-containinggas (air) that is supplied is adjusted) in order to adjust thetemperature of the reaction chamber 4A, but as shown below, it is alsopossible to perform this adjusting operation automatically.

In this separate embodiment, as shown in FIG. 14, a multi-pointtemperature sensor 12 that detects the temperature, such as Tin (inlettemperature), Tmax (maximum temperature), and Tout (outlet temperature),within the reaction chamber of the low-temperature reforming portion 1,and control means 11 that performs control to adjust the ratio of theamount of at least one of the oxygen-containing gas, steam, and carbondioxide-containing gas that is supplied with respect to the hydrocarbonfuel based on the information detected by the temperature 12 areprovided. Reference numerals 13 a to 13 e in the drawing denoteelectromagnetic valves for adjusting the flow rate of the respectivegas.

Then, for example based on the maximum temperature Tmax of the reformingreaction region within the reaction chamber, the control means 11adjusts at least one of the amount of oxygen-containing gas, the amountof the steam-containing gas, and the amount of the carbondioxide-containing gas with respect to the amount of hydrocarbon fuelthat is supplied, performing control such that the thermal decompositionindex temperature of the fuel, which is established based on the typeand concentration of the hydrocarbons within the fuel, becomes the upperlimit of the temperature in the reforming reaction region within thereaction chamber. In particular, if Tmax of the reaction chamber exceedsthe thermal decomposition index temperature of the fuel, then either theratio of the supply amount of at least one of the steam-containing gasand the carbon dioxide-containing gas is increased or the ratio of thesupply amount of the oxygen-containing gas is reduced, to cool thereaction chamber.

Further, in the reformed gas production apparatus of the invention, aswith the early stage low-temperature reforming portion 1 (reactionchamber) it is also possible to change the ratio of the amount of atleast one of the oxygen-containing gas, the steam, and the carbondioxide-containing gas that is supplied to the later stagehigh-temperature reforming portion 2 (second reaction chamber) withrespect to the reformed gas in order to adjust the temperature of thesecond reaction chamber.

It should be noted that, although not shown, the later stage reformingportion (high-temperature reforming portion 2), like the early stagereforming portion (low-temperature reforming portion 1), can also beprovided with a configuration in which, based on the informationdetected by a temperature sensor that detects the temperature Tmaxwithin the second reaction chamber, a control means performs control tochange the ratio of the amount of at least one of the oxygen-containinggas, the steam, and the carbon dioxide-containing gas that is suppliedto the high-temperature reforming portion 2 with respect to the firstreformed gas in order to adjust the temperature of the second reactionchamber.

Further, an actual reforming apparatus could also be provided with atemperature adjustment mechanism 15 that is capable of forcibly coolingor heating the early stage low-temperature reformer 1 (reaction chamber)from the outside, and a second temperature adjustment mechanism 15 thatis capable of forcibly cooling or heating the later stagehigh-temperature reformer 2 (second reaction chamber) from the outside.Specifically, as illustratively shown in FIG. 16, the temperatureadjustment mechanism 15 for the low-temperature reformer 1 (reactionchamber) and the second temperature adjustment mechanism 15 for thehigh-temperature reformer 2 (second reaction chamber) both are made of agas burner 15A for heating and a cooling tube 15B through which acooling fluid is passed to cause a cooling effect.

The temperature adjustment mechanisms 15 can also be configured suchthat they automatically perform a control to cool the reaction chamberif based on the temperature sensor 11 shown in FIG. 14 it is determinedthat the maximum temperature of the reforming reaction region hasexceeded the thermal decomposition index temperature of the fuel.

Further, as shown in FIG. 15, the reformed gas production apparatus ofthe present invention can also be provided with a detector 16 thatdetects the type and the concentration of the hydrocarbons in the fuelthat is supplied to the early stage low-temperature reforming portion 1(reaction chamber), and control means 11 that performs control to derivethe thermal decomposition index temperature of that fuel from therelationship between the type and the concentration of the hydrocarbons,such as that shown in FIG. 19, based on the information detected by thedetector 16.

If it is determined that the Tmax (maximum temperature) in the reformingreaction region of the low-temperature reforming portion 1 that isdetected by the temperature sensor 12 has exceeded the thermaldecomposition index temperature, which is set based on the detector 16,then the control means 11 controls the electromagnetic valves 13 a to 13e for adjusting the flow of the respective gases to either increase thesupply amount ratio of at least one of the steam-containing gas and thecarbon dioxide-containing gas or reduce the supply amount ratio of theoxygen-containing gas, or alternatively controls the temperatureadjustment mechanism 15 in order to cool the low-temperature reformingportion 1 (reaction chamber). By running the reactions with the thermaldecomposition index temperature serving as the upper limit temperaturein this way, it is possible to realize a reforming operation that hasexcellent reactivity yet that is without problem.

It should be noted that there are no particular limitations regardingthe detector 16 for detecting the type and the concentration of thehydrocarbons, and for this it is possible to use a conventional,publicly available sensor, for example. Also, if the composition of thefuel to be used is known beforehand, then it is also possible to specifythe type of the hydrocarbons detected and for the detector 16 to detectonly the concentration of those.

With this reformed gas production apparatus it is possible to derive theideal thermal decomposition index temperature even if the type orcomposition of the fuel that is supplied changes, and thus it ispossible to prevent thermal decomposition of the fuel.

In the foregoing embodiments, the reforming catalyst and the secondreforming catalyst used a metal that has the ability to reform steam,and normally has the ability to reform steam as well as a the ability tocause partial oxidation.

INDUSTRIAL APPLICABILITY

The reformed gas production method and the reformed gas productionapparatus according to the present invention can be employed in thefield of synthesis gas production, such as in the production of liquidfuel from natural gas (GTL), and in the field of hydrogen production forfuel cells, for example.

The invention claimed is:
 1. A reformed gas production apparatuscomprising: a reaction chamber containing a reforming catalyst; a supplyroute connected to a fuel source that contains a plurality of types ofhydrocarbons and configured to supply a fluid that includes a fuelcontaining a hydrocarbon having at least two carbon atoms, at least oneof steam and a carbon dioxide-containing gas, and an oxygen-containinggas, to the reaction chamber; a reformed gas conduction route configuredto conduct a reformed gas that is produced through a reforming reactionand that includes methane, hydrogen, and carbon monoxide, from thereaction chamber; and reaction chamber temperature control meansprogrammed to control a temperature of the reaction chamber; wherein thefuel is a mixed fuel that contains a plurality of types of hydrocarbonseach having at least two carbon atoms; and wherein the reaction chambertemperature control means is programmed to regard the thermaldecomposition index temperature of the fuel, which is a value of thelowest thermal decomposition temperature of the plurality of types ofhydrocarbons that make up the fuel, the thermal decompositiontemperature being determined based on a gas type and a concentration ofhydrocarbons having at least two carbon atoms that make up the fuel, asan upper limit temperature of the reforming reaction region, and in acase where the maximum temperature in the reforming reaction regionexceeds the upper limit temperature, the reaction chamber temperaturecontrol means performs control to cool the reaction chamber.
 2. Thereformed gas production apparatus according to claim 1, wherein a valueof the lowest temperature of the thermal decomposition temperatures thatare found based on a concentration in the fuel of at least two types ofhydrocarbons of the hydrocarbons having at least two carbon atoms thatmake up the fuel is selected as the thermal decomposition indextemperature of the fuel.
 3. The reformed gas production apparatusaccording to claim 1, wherein the fuel contains at least 50% methane. 4.The reformed gas production apparatus according to claim 1, wherein thefuel is a natural gas, and the thermal decomposition index temperatureof the fuel is set to the value of the lowest temperature of the thermaldecomposition temperatures that are found based on a concentration inthe fuel of hydrocarbons having from 2 to 5 carbon atoms that make upthe fuel.
 5. The reformed gas production apparatus according to claim 1,wherein the concentration is the hydrocarbon concentration of the fuelat an inlet portion of the reaction chamber.
 6. The reformed gasproduction apparatus according to claim 1, wherein a temperature sensorthat detects the temperature of the reforming reaction region, andcontrol means that controls the temperature of the reaction chamber byadjusting a supply amount ratio of at least one of the oxygen-containinggas, the steam, and the carbon dioxide-containing gas with respect tothe fuel based on the information detected by the temperature sensor,are provided as the reaction chamber temperature control means.
 7. Thereformed gas production apparatus according to claim 1, furthercomprising: a temperature adjustment mechanism that is capable ofcooling or heating the reforming reaction region.
 8. The reformed gasproduction apparatus according to claim 1, further comprising: detectionmeans that detects a type and a concentration of hydrocarbons having atleast two carbon atoms that make up the fuel that is supplied to thereaction chamber; and thermal decomposition index temperature derivationmeans that derives the thermal decomposition index temperature of thefuel based on the type and the concentration of the hydrocarbonsdetected by the detection means.
 9. The reformed gas productionapparatus according to claim 1, further comprising: a desulfurizingapparatus before the reaction chamber that desulfurizes at least one ofthe fuel, the oxygen-containing gas, the steam, and the carbondioxide-containing gas.
 10. The reformed gas production apparatusaccording to claim 1, further comprising: a second reaction chamber thatcontains a second reforming catalyst and that produces a second reformedgas that includes hydrogen and carbon monoxide through a secondreforming reaction of the reformed gas that has been conducted from thereaction chamber; wherein a maximum temperature in the second reformingreaction region of the second reaction chamber is maintained within atemperature range of 400 to 1200° C., and an outlet temperature of thesecond reaction chamber is adjusted such that it is higher than anoutlet temperature of the reaction chamber.
 11. The reformed gasproduction apparatus according to claim 1, wherein the reformed gasproduction apparatus is used in mobile and stationary applicationsalike.